Fuel lances of this kind are used for example in burners which can be operated both with liquid fuel and also with gaseous fuel. As a rule, the lance is provided for operation with the liquid fuel, for example oil. The oil then flows through the lance and emerges at its tip through oil nozzles into a combustion chamber. After egress from the nozzle the oil is burned in the combustion chamber, into which compressor air is also introduced. Gaseous fuels on the other hand are frequently injected into an air feed channel surrounding the nozzle lance, and there mixed with compressor air, before the mixture is introduced into the combustion chamber.
In the case of operation with gaseous fuels, the lance tip is as a rule subject to high temperatures in the area of up to approx. 1000° C. as a result of the proximity of the flame. These high temperatures can lead to a carbonization of residues of liquid fuel in the nozzle lance. Accordingly, before switching the burner to operation with a liquid fuel a scavenging of the fuel passages in the fuel lance with cooling water generally takes place, in order to flush away possible deposits. The temperature of the cooling water however stands at only approx. 25° C., which can lead to a thermal shock in the hot fuel lance. High temperature gradients thereby arise in the area of the nozzles, so that considerable thermal stresses can occur in the lance tip. Through the repeated occurrence of such thermal stresses, splits in the area of the nozzles may ensue, whereby the start values and thus the useful life of the fuel nozzle are reduced.
US 2001/0042798 A1 discloses a fuel lance with a tip, having a nozzle surface with two fuel nozzles, where the nozzle surface between the fuel nozzles is provided with slots.
US 2006/0027232 A1 discloses a fuel lance with slots.
EP 1760403 A2 discloses fuel nozzles for gas turbines.